Antirotated piston rack

ABSTRACT

A valve skirt is connected to a shaft. The shaft extends in a rearward direction away from the skirt and has rack teeth at a location spaced away from the skirt. A tab is positioned between the skirt and the rack teeth, and has at least one flat surface. A rack support supports the rack for axial movement, and the rack support has a support ear that has a flat surface engaging the flat surface on the rack to prevent relative rotation of the rack when driven by a pinion gear. An air starter valve, a gas turbine engine and a method are also disclosed.

BACKGROUND OF THE INVENTION

This application relates to a rack and pinion connection for use in amanual wrench drive for an air starter valve.

Air starter valves are known, and are utilized in conjunction with gasturbine engines to provide air to the starter when the engine is beingstarted. The flow of air to the starter is stopped by the starter airvalve once the engine has started.

In one known air starter valve, a manual wrench drive allows movement ofthe valve for maintenance, or for repair. The valve is normally moveableupon control of a solenoid valve. However, should the valve fail, themanual wrench drive can also move the valve to an open position.

The manual wrench drive typically drives rotation of a pinion gear whichin turn drives rack teeth associated with a shaft to move a valve skirt.The rack has generally been machined into a cylindrical portion of theshaft which is connected to the valve skirt. The valve skirt, shaft, andrack, as a unit, were able to rotate relative to the housing.

SUMMARY OF THE INVENTION

A valve skirt is connected to a shaft. The shaft extends in a rearwarddirection away from the skirt and has rack teeth at a location spacedaway from the skirt. A tab is positioned between the skirt and the rackteeth, and has at least one flat surface. A rack support supports therack for axial movement, and the rack support has at least one supportear that has a flat surface engaging the flat surface on the rack toprevent relative rotation of the rack when driven by a pinion gear. Anair starter valve, a gas turbine engine and a method are also disclosed.

These and other features of the present invention will be bestunderstood from the following specification and drawings, the followingof which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an air starter valve in a closed position.

FIG. 1B shows the FIG. 1A valve in an open position.

FIG. 2A shows detail of a manual drive arrangement with the valve in theclosed position.

FIG. 2B shows the FIG. 2A valve detail in the open position.

FIG. 3 is a detail of a rack support.

FIG. 4 is a detail of a rack and shaft.

FIG. 5 shows further details of the FIG. 4 rack and shaft.

DETAILED DESCRIPTION

An air starter valve 20 supplies air from an air source 22 to a gasturbine engine starter 24, as illustrated in FIG. 1A, at start-up of agas turbine engine. As shown, a valve skirt 28 moves relative to aninternal piston housing 39 to block or allow flow between an outersurface of the skirt 28 and a housing 200. As shown in FIG. 1A, aforward end 100 of the skirt is sealed against the housing 200, and airwill not flow to the starter 24. This position is obtained since the airfrom the source 22 acts against a rear face of the skirt 28 and drivesit to the left in this Figure. A solenoid 32 communicates with a control31 to cause the opening and closing of the valve skirt 28, as desired.The control 31 may be an electronic control which is programmed toprovide air to the starter 24 from the source 22. Solenoid 32 controlsthe connection of a path 33 of pressurized air from source 22 through aline 36, and into an outlet 38 in a chamber 101. As will be explained,this will drive the skirt 28 to an open position (see FIG. 1B).Alternatively, the solenoid 32 can be moved to a position whichcommunicates the connection 36 to atmosphere at 34. In this position,the pressurized air from the source 22 will drive the valve skirt 28 tothe closed position (FIG. 1A).

When it is desired to open the valve, solenoid 32 moves to allow supplyof the pressurized air from tap 33 through a line 36 to an internalchamber 101 defined between the housing 39 and the skirt 28, and througha fluid connection 38. When pressurized air is delivered into thischamber, it forces skirt 28 to the right as shown in this Figure suchthat forward end 100 no longer seals against the housing 200. In thisposition, air can flow from source 22 to the starter 24.

Under certain conditions, it is desirable to manually move the pistonbetween the open and closed position. Thus, a manual wrench connection42 is provided to turn a pinion gear 46, and drive a rack 44 to moveshaft 40, and hence the valve skirt 28.

As shown in FIG. 2A, the rack teeth 44 are positioned adjacent to a tab60. Tab 60 is guided between support ears 58 which extend on opposedsides of the tab 60. The ears 58 are part of a rack support 54. Racksupport 54 has a pin locating slot 56 which receives a pin 158 from anouter housing 26 to ensure that the rack support 54 is properly locatedcircumferentially, and properly guides the tab 60 between the ears 58for axial movement while limiting relative rotation.

As can be seen, the support 54 is positioned between the valve skirt 28and the pinion gear 46. In the position shown in FIG. 2A, tab 60 isspaced from the support 54. This is the closed position.

In FIG. 2B, the valve skirt 28 has moved to the open position and thetab 60 rests adjacent the support 54.

FIG. 3 shows detail of the support 54, including a slot 64 in arearwardly extending cylindrical portion 66. Slot 64 provides access tothe rack teeth 44 for the pinion gear 46. Further, the ears 58 haveslots 62. Finally, the locating slot 56 is shown.

FIG. 3 shows support 54, d₁ is defined as the distance between internalsurfaces of the ears 58. A width of the ears, d₂, is measured parallelto flat sides 102 (see FIG. 5) of tab 60. In one embodiment, d₁ was0.614″ (1.56 cm) and d₂ was 1.000″ (2.54 cm).

FIG. 4 shows the combined part 302 with shaft 40 integral to a portion41 that receives rack teeth 44. A distance d₃ is defined between arearward (i.e., facing away from rack teeth 44) surface 300 of anenlarged plate 400 that abuts a surface in valve skirt 28 (see FIGS. 1Aand 1B), and a forward end 301 of combined part 302. Plate 400 issecured to skirt 28. A distance d₄ is defined between the surface 300and a rearward surface 303 of tab 60. A distance d₅ is defined betweenthe surface 300 and a forward surface 304 of tab 60. In one embodimentd₃ was 4.280″ (10.87 cm), d₄ was 1.880″ (4.78 cm) and d₅ was 2.005 (5.09cm). In embodiments, a ratio of d₃ to d₄ was between 2.27 and 2.28 and aratio of d₃ to d₅ was between 2.13 and 2.14.

FIG. 5 is a front view of part 302, showing tab 60. The distance betweenthe flat sides 102 of the tab 60 is defined as d₆. The top and bottomends of the tab 60 are curved along cylindrical sections 401, and adiameter D₁ is defined between those cylindrical sections 401. In oneembodiment, D₁, was 1.166″ (2.96 cm) and d₆ was 0.596″ (1.51 cm). Inembodiments, a ratio of D₁ to d₂ was between 1.12 and 1.22. A ratio ofd₁ to d₆ was between 1.02 and 1.04.

In a method, a part 302 and rack support 54, including details asdefined above, are mounted into an air starter valve.

Although embodiments have been disclosed, a worker of ordinary skill inthis art would recognize that certain modifications would come withinthe scope of this invention. For that reason, the following claimsshould be studied to determine the true scope and content of thisinvention.

1. A valve comprising: a valve skirt connected to a shaft, said shaftextending in a rearward direction away from said skirt and having rackteeth at a location spaced away from the skirt, a tab positioned betweensaid valve skirt and said rack teeth, said tab having at least one flatsurface; and a rack support supporting said rack for axial movement,said rack support having at least one ear with a flat surface engagingsaid at least one flat surface on said rack to limit relative rotationof said rack.
 2. The valve as set forth in claim 1, wherein there are apair of opposed flat surfaces on said tab, with said tab having partcylindrical sections connecting the opposed flat surfaces of said tab,and said rack support having a pair of ears with flat surfacessupporting said pair of flat surfaces on said rack.
 3. The valve as setforth in claim 2, wherein a ratio of a distance between internal facingsurfaces of said pair of ears, and a distance between said pair of flatsurfaces on said tab is between 1.02 and 1.04.
 4. The valve as set forthin claim 3, wherein a part cylindrical diameter is defined between saidpart cylindrical sections of said tab and a width of said ears ismeasured parallel to said opposed flat surfaces, and a ratio of saidpart cylindrical diameter to said width of said ears is between 1.12 and1.22.
 5. The valve as set forth in claim 1, wherein an enlarged plate isdefined on said shaft, with a plate distance defined between an end ofsaid shaft beyond said rack teeth, and a face of said first plate facingaway from said rack teeth, and a plate spacing distance defined betweena first face of said tab, facing away from said rack teeth, and saidface of said plate, and a ratio of said plate distance to said platespacing distance being between 2.27 and 2.28.
 6. The valve as set forthin claim 5, wherein a second face of said tab faces said rack teeth, anda facing distance is defined between said face of said plate and saidsecond face of said tab, and a ratio of said plate distance to saidfacing distance is between 2.13 and 2.14.
 7. The valve as set forth inclaim 1, wherein said rack support has a pin locating slot to receive apin from an outer housing to ensure said rack support is properlypositioned.
 8. An air starter valve comprising: a valve skirt connectedto a shaft, said shaft extending in a rearward direction away from saidskirt and having rack teeth at a location spaced away from said skirt, atab positioned between said valve skirt and said rack teeth, said tabhaving at least one flat surface, a rack support supporting said rackfor axial movement, said rack support having an ear with a flat surfaceengaging said at least one flat surface on said rack to limit relativerotation of said rack when said rack; and a manual wrench drive, saidmanual wrench drive allowing rotation of a pinion, said pinion engagingsaid rack teeth to allow manual movement of said rack, said shaft andsaid skirt.
 9. The air starter valve as set forth in claim 8, whereinthere are a pair of flat surfaces on said tab, with said tab having partcylindrical sections connecting the opposed flat surfaces of said tab,and said tab support having a pair of ears with one of said opposed flatsurfaces supporting each of said pair of flat surfaces on said rack. 10.The air starter valve as set forth in claim 9, wherein a ratio of adistance between internal facing surfaces of said pair of ears, and adistance between said pair of flat surfaces on said tab is between 1.02and 1.04.
 11. The air starter valve as set forth in claim 10, wherein apart cylindrical diameter is defined between said part cylindricalsections of said tab and a width of said ears is measured parallel tosaid opposed flat surfaces, and a ratio of said part cylindricaldiameter to said width of said ears is between 1.12 and 1.22.
 12. Theair starter valve as set forth in claim 7, wherein an enlarged plate isdefined on said shaft, with a plate distance defined between an end ofsaid shaft beyond said rack teeth, and a face of said plate facing awayfrom said rack teeth, and a plate spacing distance defined between afirst face of said tab, facing away from said rack teeth, and said faceof said plate, and a ratio of said plate distance to said plate spacingdistance being between 2.27 and 2.28.
 13. The air starter valve as setforth in claim 12, wherein a second face of said tab faces said rackteeth, and a facing distance is defined between said face of said plateand said second face of said tab, and a ratio of said plate distance tosaid facing distance is between 2.13 and 2.14.
 14. The air starter valveas set forth in claim 8, wherein said rack support has a pin locatingslot to receive a pin from an outer housing to ensure said rack supportis properly positioned.
 15. A gas turbine engine comprising: a starterand a turbine; a source of air connected to an air starter valve forsupplying air to said starter when said gas turbine engine is started;and the air starter valve having a valve skirt connected to a shaft,said shaft extending in a rearward direction away from said skirt andhaving rack teeth at a location spaced away from said skirt, a tabpositioned between said valve skirt and said rack teeth, said tab havingat least one flat surface, a rack support supporting said rack for axialmovement, said rack support having an ear with a flat surface engagingsaid at least one flat surface on said rack to limit relative rotationof said rack when said rack, and a manual wrench drive, said manualwrench drive allowing rotation of a pinion, said pinion engaging saidrack teeth to allow manual movement of said rack, said shaft and saidskirt.
 16. The gas turbine engine as set forth in claim 15, whereinthere are a pair of flat surfaces on said tab, with said tab having partcylindrical sections connecting the opposed flat surfaces of said tab,and said rack support having a pair of ears with one of said opposedflat surfaces supporting each of said pair of flat surfaces on saidrack.
 17. The gas turbine engine as set forth in claim 16, wherein aratio of a distance between internal facing surfaces of said pair ofears, and a distance between said pair of flat surfaces on said tab isbetween 1.02 and 1.04.
 18. The gas turbine engine as set forth in claim17, wherein a part cylindrical diameter is defined between said partcylindrical sections of said tab and a width of said ears is measuredparallel to said opposed flat surfaces, and a ratio of said partcylindrical diameter to said width of said ears is between 1.12 and1.22.
 19. The gas turbine engine as set forth in claim 13, wherein anenlarged plate is defined on said shaft, with a plate distance definedbetween an end of said shaft beyond said rack teeth, and a face of saidplate facing away from said rack teeth, and a plate spacing distancedefined between a first face of said tab facing away from said rackteeth and said face of said plate, and a ratio of said plate distance tosaid plate spacing distance being between 2.27 and 2.28.
 20. The gasturbine engine as set forth in claim 19, wherein a second face of saidtab faces said rack teeth, and a facing distance is defined between saidface of said plate and said second face of said tab, and a ratio of saidplate distance to said facing distance is between 2.13 and 2.14.
 21. Thegas turbine engine as set forth in claim 15, wherein said rack supporthas a pin locating slot to receive a pin from an outer housing to ensuresaid rack support is properly positioned.
 22. A method of replacing arack and shaft in an air starter valve including the steps of:connecting a shaft to a valve skirt, said shaft having rack teeth, andmoving a pinion gear to engage said rack teeth; and said shaft extendingin a rearward direction away from said skirt and having rack teeth at alocation spaced away from the skirt, a tab positioned between said valveskirt and said rack teeth, said tab having at least one flat surface,and a rack support supporting said rack for axial movement, said racksupport having an ear with a flat surface engaging said at least oneflat surface on said rack to prevent relative rotation of said rack.